A TDM interface is a highly synchronous system that is used to bi-directionally transport a number of different independent data channels. For example, a T1 line contains a TDM serial data stream formatted in frames each containing data for 24 channels. For a T1 line, within each 125 .mu.sec. TDM frame, each of the 24 sub-frames contains 8 bits of data for the corresponding channel thus defining a data rate per channel on the T1 line of 64 Kbits/sec. Any prior art device that processes one of those TDM channels must remain synchronized to the T1 reference clock to avoid any data loss from `frame slips` in either the upstream or the downstream direction. Thus, a TDM switch is generally used to receive/send the data from/to the data stream on the T1 line, to derive a clock signal from the highly accurate data rate on the T1 line, and to then distribute a clock signal synchronized to the clock rate of the T1 line and individual channels of data to various processing devices to terminate the data from each channel for delivery via a digital local bus to one or more host computers. Similarly, since this is a bidirectional system, the TDM switch formats data from the various processing devices into the expected TDM format for delivery upstream on the TDM bus. This interchange of upstream and downstream data is performed in a handshake manner i.e., a simultaneous transfer of one up-stream TDM frame for each downstream TDM frame.
The prior art provides the interface between a TDM serial data stream on a highly deterministic signal bus and a parallel local bus through manipulation of the signals in the TDM data stream. This requires the use of a highly accurate synchronous clock that matches the highly accurate rate of the signals in the TDM data stream and the use of cross-bar switches to direct each of the 24 channels of data to or from the TDM bus. This is necessary to keep all of the signals from the 24 TDM bus channels synchronized. Such prior art systems are very hardware intensive.
It would be advantageous to perform more functions in such a system that are today performed with dedicated hardware with microprocessors and software. If that were done, the amount of hardware needed for these systems would be reduced, and thus costs would be reduced. Additionally, the hardware that is needed is simplified since it is not embedded in the TDM bus structure with all of the accurate timing demands necessary to process the TDM signals. In addition, the user would only need to purchase a T1/E1 interface unless the application requires additional functionality. The various embodiments of the present invention provide such implementations.